There is a continuing trend towards increasing the energy and performance of gun and rocket propellants. Thus, nitrocellulose-based propellants are gradually being replaced by propellants containing high energy organic nitramines, such as RDX (1,3,5-trinitro-1,3,5-triazacyclohexane) and HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane). Typical nitramine type propellants may consist of 60 to 80 weight percent of RDX or HMX and the remainder being composed of an energetic binder, such as nitrocellulose, or an "inert" (i.e. low energy) binder such as cellulose acetate or polyurethane. Further, a typical nitramine propellant has a burn rate of 1 cm/s at 5 MPa (725 psi), 9 cm/s at 50 MPa (7,250 psi) and 70 cm/s at 500 MPa (72,500 psi). Due to binder suppression effects, the burn rate at low pressure (below 20 or 30 MPa) for inert binders and/or nitramine particle sizes of more than a few microns may fall below these values. For many years attempts have been made to reduce or eliminate such low pressure binder suppression effects (and the resulting "slope breaks" in the burn rate vs. pressure curves) to decrease the pressure dependence of the burn rate or to increase the burn rate over a large pressure range.
Higher burn rates would be desirable for both rocket and gun applications, since they would require a smaller burning surface area for a given gas generation rate, which in turn would permit a larger propellant "web". This would make not only the grain manufacture more economical, but also would make it possible to design more efficient and reliable rocket engines as well as guns with greater ballistic efficiency and hence higher muzzle velocities for a given peak chamber pressure.
Prior to the present invention all reported attempts to increase the burning rates of nitramine propellants with "catalysts" have been only marginally successful at best. This is particularly true for the cyclic nitramines such as RDX and HMX which seem very immune to catalytic effects. Most attempts to catalyze nitramines have involved metal salts, since many of them are known to be effective with nitrocellulose-based propellants. Generally, the anions have been oxygen (metal oxides), halides (F, Cl, Br), organics (e.g. oxalates, salicylates) or inorganic oxidizers (e.g. NO.sub.3, ClO.sub.4). All of these anions can be considered to be oxidizers, since they either contribute oxygen or take up hydrogen. Thus, for example, A. P. Glaskova "The Effect of Catalysts on the Combustion of Explosives", Combustion, Explosive and Shock Waves, 10(3), 281-90(1974) investigated the effect of a large number of additives on the burn rate of RDX, including NaF, CuCl, KClO.sub.4, KNO.sub.3, cobalt-and copper oxalate and sodium salicylate, and found that none of them increased the burn rate noticeably. B. B. Goshgarian, "Chemical Ingredient Studies Task II-HMX Additive Studies" , Air Force Rocket Propulsion Laboratory, Technical Report 79-59(July 1979) found that propellants made with HMX coated with ammonium perchlorate or (CH.sub.3).sub.4 NNO.sub.3 had higher burn rates at low pressure. However, the increase was less than a factor of two and was present only in the 3.45-20.7 MP.sub.a (500-3000 psi) region. K. P. McCarty, "HMX Propellant Combustion Studies," Air Force Rocket Propulsion Laboratory, Technical Report 79-61 (November 1979) found that some burn rate acceleration below 7 MP.sub.a (1000 psi) was obtained for a 50%-HMX-50% double based propellant by addition of Pb.sub.2 O.sub.3 and a mixture Pb.sub.2 O.sub.3 and SnO.sub.2, but that no burn rate increase was found when the HMX content was increased to 70% or if an inert binder was employed. The catalysis observed with the double base energetic binder was probably due simply to catalysis of the nitrocellulose in the binder, since Pb.sub.2 O.sub.3 is known to be an effective catalyst for nitrocellulose and double base propellants.
Accordingly, it appears that prior to the present invention, no catalysts have been shown to be capable of accelerating the burn rate of nitramines and nitramine propellants except under very low pressure conditions where the binder controls the burn rate.